The exposure of a subject in the far field of radiofrequency sources operating in the 10-900-MHz range has been studied. The electromagnetic field inside an anatomical heterogeneous model of the human body has been computed by using the finite-difference time-domain method; the corresponding temperature increase has been evaluated through an explicit finite-difference formulation of the bio-heat equation. The thermal model used, which takes into account the thermoregulatory system of the human body, has been validated through a comparison with experimental data. The results show that the peak specific absorption rate (SAR) as averaged over 10 g has about a 25-fold increase in the trunk and a 50-fold increase in the limbs with respect to the whole body averaged SAR (SAR/sub WB/). The peak SAR as averaged over 1 g, instead, has a 30- to 60-fold increase in the trunk, and up to 135-fold increase in the ankles, with respect to SAR/sub WB/. With reference to temperature increases, at the body resonance frequency of 40 MHz, for the ICNIRP incident power density maximum permissible value, a temperature increase of about 0.7/spl deg/C is obtained in the ankles muscle. The presence of the thermoregulatory system strongly limits temperature elevations, particularly in the body core.

Specific absorption rate and temperature elevation in a subject exposed in the far-field of radio-frequency sources operating in the 10-900-MHz range

Health Effects of Depleted Uranium on Exposed Gulf War Veterans

We have used the finite-difference time-domain (FDTD) method to calculate induced current densities in a 1.31-cm (nominal 1/2 in) resolution anatomically based model of the human body for exposure to purely electric, purely magnetic, and combined electric and magnetic fields at 60 Hz. This model based on anatomic sectional diagrams consists of 45,024 cubic cells of dimension 1.31 cm for which the volume-averaged tissue properties are prescribed. It is recognized that the conductivities of several tissues (skeletal muscle, bone, etc.) are highly anisotropic for power-line frequencies. This has, however, been neglected in the first instance and will be included in future calculations. Because of the quasi-static nature of coupling at the power-line frequencies, a higher quasi-static frequency f' may be used for irradiation of the model, and the internal fields E' thus calculated can be scaled back to the frequency of interest, e.g., 60 Hz. Since in the FDTD method one needs to calculate in the time domain until convergence is obtained (typically 3-4 time periods), this frequency scaling to 5-10 MHz for f' reduces the needed number of iterations by over 5 orders of magnitude. The data calculated for the induced current and its variation as a function ofmore » height are in excellent agreement with the data published in the literature. The average current densities calculated for the various sections of the body for the magnetic field component (H) are considerably smaller (by a factor of 20-50) than those due to the vertically polarized electric field component when the ratio E/H is 377 ohms. We have also used the previously described impedance method to calculate the induced current densities for the anatomically based model of the human body for the various orientations of the time-varying magnetic fields, namely from side to side, front to back, or from top to bottom of the model, respectively. 34 refs.« less

Numerical dosimetry at power-line frequencies using anatomically based models.

A public health statement summarizes information about a hazardous substance. The information is taken from a toxicological profile developed by ATSDR’s Division of Toxicology and Human Health Sciences (DTHHS). A toxicological profile is a thorough review of a hazardous substance.This toxicological profile examines uranium. This public health statement summarizes the DTHHS findings on uranium, describes the effects of exposure to it, and describes what you can do to limit that exposure.

Toxicological profile for uranium

Distribution of uranium in rats implanted with depleted uranium pellets

Uranium concentrations were radiochemically determined in samples of lung, kidney, liver and bone collected at autopsy from an occupationally exposed individual. Levels of U in these tissues were clearly in excess of those expected from environmental exposure. Deposition followed the pattern: skeleton greater than liver greater than kidney, with ratios of 63:2.8:1. The data suggest there is an important long-term storage depot in the skeleton, but the fraction transferred to this compartment, as proposed by ICRP 30, may be too small. In vivo chest counts obtained over about a 10-y period prior to death indicated about a factor of 2 greater in total U content and /sup 235/U enrichment than deposition estimates made at autopsy for the lungs and associated lymph nodes.

Uranium in the tissues of an occupationally exposed individual.

Distribution of Plutonium and Americium in Whole Bodies Donated to the United States Transuranium Registry

The content of /sup 238/Pu, /sup 239/Pu and /sup 241/Am in the liver and skeleton was estimated from radiochemical analysis of human liver and bone samples obtained at autopsy from former actinide workers whose occupational histories were suggestive of chronic inhalation exposures, with minor skin contamination and wounds documented in a few individuals. For times estimated to be several years to a few decades post intake, 75.8 +/- 15.3% of the total /sup 241/Am in the skeleton and liver was found in the skeleton (25 cases) as compared with 63.4 +/- 24.1% for /sup 238/Pu (36 cases) and 53.2 +/- 18.2% for /sup 239/Pu (43 cases). These differences are significant at the 95% confidence level. Of these cases, 34 included data on both /sup 238/Pu and /sup 239/Pu and were divided into high and low activity subgroups. The difference in the fractionation of the two Pu isotopes was apparent only in the low activity subgroup, suggesting that the difference observed between the Pu isotopes may be an artifact of the data. The different partitioning of these three nuclides suggests that the ALIs for /sup 238/Pu and /sup 241/Am may be high by about 25-50% if only the dose to bonemore » is considered and may be high by 12-13%, based on the weighted committed dose equivalent in target organs or tissues.« less

Partitioning of 238Pu, 239Pu and 241Am in skeleton and liver of U.S. Transuranium Registry autopsy cases.

Three human half-skeletons were radiochemically analysed by the United States Transuranium Registry (USTR) for 239Pu+240Pu and 241Am and another was analysed for 241Am only. The distribution of activity in individual bones or groups of bones has been characterised as a percentage of the total skeletal content and compared with published distributions reported for primates (baboons and monkeys) and human injection cases. Americium and plutonium distributions in the four skeletons were similar; however, there was somewhat less variability in the plutonium data for the individual bones. In humans, the skull, tarsals (as a group), humeri, scapulae and patellae contained the most consistent percentages of the total skeletal activity and can be individually used to estimate total skeletal content. The patella is particularly suitable because of the ease with which this bone can be obtained at autopsy. The greatest variations in the fraction of the total skeletal activity were found in the mandible, sacrum, coccyx and sternum.

Macrodistribution of plutonium and americium in four human skeletons

Radiochemical analysis of two half skeletons donated to the United States Transuranium Registry from individuals with occupationally incurred depositions, one of /sup 241/Am and the other of /sup 239/Pu, revealed an inverse proportionality between the concentration of actinide in the bone ash and the fraction of ash (or the calcium content of the ash). A similar relationship was observed in a third case suffering from osteoporosis, but the slope was shallower. These results suggest that accurate estimates of the total skeletal content of actinide can be made from radiochemical analysis of only a few bone samples.

J.F. McInroy

Papers

Uranium in the tissues of an occupationally exposed individual.

Distribution of Plutonium and Americium in Whole Bodies Donated to the United States Transuranium Registry

Partitioning of 238Pu, 239Pu and 241Am in skeleton and liver of U.S. Transuranium Registry autopsy cases.

Macrodistribution of plutonium and americium in four human skeletons

Actinide distribution in the human skeleton.